What do the letters in plywood grades mean?
Each plywood panel carries two letters: the first rates the face veneer, the second the back. They grade appearance, not strength. A is near-flawless and paintable, B is sound with minor repairs, C is a working surface with tight knots, and D is utility veneer meant to stay hidden. So an A-C panel has a clean A face and a rough C back.
Is CDX a grade of plywood?
Not exactly. CDX is a C-face, D-back panel built with an exterior glue bond — the X marks the adhesive, not a grade. It means the panel tolerates moisture and wet-dry cycling during construction. It does not mean the panel is rated for permanent outdoor exposure; for that you move to a marine or film-faced specification.
What is the difference between A-grade and B-grade plywood?
An A face is smooth, sanded, and effectively free of open defects, with neat, minimal repairs — it takes paint and clear finish cleanly. A B face is still sound but slightly more worked, allowing small tight knots and a few patches within the grade. A is for show surfaces; B suits paint-grade and visible utility work.
Which plywood grade should I use for subfloor and sheathing?
CDX or a C-D panel is the standard choice. Both give the structural rating these jobs need, and CDX adds an exterior glue bond that survives the weather before the roof and floor coverings go on. The faces are hidden in service, so appearance grade beyond C-D adds cost without benefit.
Are the knots and patches in C and D grade plywood defects?
No. Tight knots, small knotholes, splits, and football patches within the limits set by the standard are grade characteristics, not faults. A C panel showing the knots its grade allows has met its specification. Genuine problems are usually handling-related — edge damage, moisture, or delamination — rather than the veneer features the grade permits.
